When you're logged into at least one* account, you can do either of the following:
The way this list/roster is displayed can be controlled by choosing "Flat list" and "Show offline friends".
The two options shown above can be accessed either from Main Menu->Friends, or simply by right-clicking anywhere in the Friends list.
Facebook* doesn't allow you (at least for now) to organize the Friends list through a client. Or to chat with any other users that are not from the list it provides - in other words, you can only chat facebook-to-facebook.
The only option is to do it from Facebook site modifying your Friends lists or removing them:
Screenshots are from YateClient version 4.0.